Activation of V(D)J recombination induces the formation of interlocus joints and hybrid joints in scid pre-B-cell lines

V(D)J recombination is the mechanism by which antigen receptor genes are as sembled. The site-specific cleavage mediated by RAG1 and RAG2 proteins gene rates two types of double-strand DNA breaks: blunt signal ends and covalent ly sealed hairpin coding ends. Although these DNA breaks are mainly resolve d into coding joints and signal joints, they can participate in a nonstanda rd joining process, forming hybrid and open/shut joints that link coding en ds to signal ends. In addition, the broken DNA molecules excised from diffe rent receptor gene loci could potentially be joined to generate interlocus joints. The interlocus recombination process may contribute to the transloc ation between antigen receptor genes and oncogenes, leading to malignant tr ansformation of lymphocytes. To investigate the underlying mechanisms of th ese nonstandard recombination events, we took advantage of recombination-in ducible cell lines derived from scid homozygous (s/s) and scid heterozygous (s/+) mice by transforming B-cell precursors with a temperature-sensitive Abelson murine leukemia virus mutant (ts-Ab-MLV). We can manipulate the lev el of recombination cleavage and end resolution by altering the cell cultur e temperature. By analyzing various recombination products in scid and s/ts-Ab-MLV transformants, we report in this study that scid cells make highe r levels of interlocus and hybrid joints than their normal counterparts. Th ese joints arise concurrently with the formation of intralocus joints, as w ell as,vith the appearance of opened coding ends. The junctions of these jo ining products exhibit excessive nucleotide deletions, a characteristic of scid coding joints. These data suggest that an inability of scid cells to p romptly resolve their recombination ends exposes the ends to a random joini ng process, which can conceivably lead to chromosomal translocations.